cDNA corresponding to the antigenome of nonsegmented negative strand RNA viruses and process for the production of such viruses

Abstract

The present invention relates, in general, to a methodology or the generation of nonsegmented negative-strand RNA viruses (Pringle, 1991) from cloned deoxyribonucleic acid (cDNA). Such rescued viruses are suitable for use as vaccines, or alternatively, as plasmids in somatic gene therapy applications. The invention also relates to cDNA molecules suitable as tools in this methodology and to helper cell lines allowing the direct rescue of such viruses. Measles virus (MV) is used as a model for other representatives of the Mononegavirales, in particular the family Paramyxoviridae.

Description

BACKGROUND OF THE INVENTION [0001] 1. Technical Field [0002] The present invention relates, in general, to a methodology for the generation of nonsegmented negative-strand RNA viruses (Pringle, 1991) from cloned deoxyribonucleic acid (cDNA). Such rescued viruses are suitable for use as vaccines, or alternatively, as vectors in somatic gene therapy applications. The invention also relates to cDNA molecules suitable as tools in this methodology and to helper cell lines allowing the direct rescue of such viruses. Measles virus (MV) is used as a model for other representatives of the Mononegavirales, in particular the family Paramyxoviridae. [0003] The invention provides the technology for construction of recombinant vaccine strains, in particular MV vaccine strains containing coding regions for the expression of epitopes or entire protein from other viruses, bacteria, or parasites. It also demonstrates that chimeric MV strains containing heterologous envelope proteins can be constructe...

AI Technical Summary

Problems solved by technology

This high toll arises primarily in developing countries, but in recent years also industrialised countries such as the USA have been affected again by measles epidemics, primarily due to incomplete adherence to immunisation programs (Clements and Cutts, 1995).

However, attempts to obtain infectious virus from cDNA clones of negative-strand RNA viruses have met with great difficulties.

An important drawback of that method (as well as the method reported for the rescue of negative-strand RNA viruses with a segmented genome) is the involvement of a helper virus which has to be separated from the rescued virus and which can interfere with the replication of the virus to be rescued.

However, in case of loosely structured, polymorphic virions typical for the members of the family Paramyxoviridae and in case of viruses yielding only relatively low titers, the presence of a helper virus would render the recovery of rescued viruses difficult and may well preclude their rescue altogether.

Furthermore, for viruses impaired in replication and / or budding by the vaccinia virus, rescue using the prior art systems might fail altogether.

Another possible drawback of the prior art systems based on the vaccinia helper virus is the high frequency of DNA recombinations occurring in the cytoplasm of vaccinia virus infected cells which might cause recombination of the plasmid bearing the anti-genomic sequence with the plasmids encoding N, P and L protein required for the helper function; this may lead to rescue of viruses containing N, P and L sequences derived in part from the helper plasmids rather than from the plasmid bearing the antigenomic sequence.

As a consequence, no rescue of a virus and not even of a minireplicon from cloned DNA is feasible with this cell line.

However, the rescue by microinjection experiments, unfortunately carried out by only one collaborator, could not be repeated, and all purportedly rescued viruses did not contain the genetic tag, as summarised in a commentary to these extremely sad and devastating events (Aldhous, 1992).

Nevertheless, in comparison with the rescue method described for RV and VSV, where about 2×107 cells are transfected to obtain one rescue event (Lawson et al., 1995; Schnell et al., 1994), the MV rescue compares well, particularly in view of the fact that the MV genome size is roughly 4.5 kb larger and thus in principle more difficult to rescue.

In contrast, killed vaccines or proteins manufactured by recombinant DNA technology are much less efficient, even by administration in various particulate forms developed recently, which are more efficient than traditionally used adjuvants.

On the other hand, most replicating vaccines constitute a possible threat, even if they are not proliferating, such as avipox vectors in humans (Baxby and Paoletti, 1992).

Complex viral vectors (e.g. based on vaccinia virus and related pox viruses, adenoviruses of herpesviruses) and bacterial vectors (e.g. based on derivatives of the agents causing tuberculosis or cholera) inherently elicit many lateral, unnecessary and / or undesired immune responses.

Second, the tight encapsidation of the genomes of Mononegavirales obviates RNA secondary structure which is very important in case of the positive-strand RNA viruses over the whole genome length to allow proper replication without annealing of the product to the template RNA strand; RNA segments encoding foreign antigens are not evolved to meet such requirements.

Advantages in comparison to existing vectors for gene therapy include their small size, thus limiting antigen reactions to a few proteins, and their complete inability to integrate into DNA and thus to transform cells.

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